1. Field of the Invention
The present invention relates to commutation and decommutation of electrical signals and more particularly to video signal commutation. 2. Description of the Prior Art
The use of time-lapse video tape recorders in surveillance and security applications has gained wide acceptance. Generally, facilities like banks and other security-sensitive installations, are remotely monitored by time-lapse television cameras individually directed to view particular sections of the facility. In this manner, unattended monitoring of individual secured areas can be made and if an intrusion is suspected the record can then be played back. Most often, however, there is more than one distinct area which requires such unattended monitoring. Thus, more than one camera is typically involved in the surveillance of a given facility. In order to conserve the recording costs and to reduce the number of tapes and the requisite storage problems associated therewith, the multiple cameras typically all store their video record, in a commutated manner, on a video storage tape. Both in order to reduce tape bulk and to allow for a wide range of camera commutation, the most frequent technique of storing on tape is by way of an input sequence where the individual camera frames are interleaved in a predetermined order. Such commutation is typically performed by a sequencing switch either in a solid state form or actually mechanically driven.
Such expansion of the monitored field of view presents, during playback, a difficult viewing sequence to the person inspecting the tapes. Specifically, if the tape is played back normally the sequential frames stored thereon present sequentially differing fields of view with a resulting loss in coherency and with a resulting reduction in the speed at which such frames can be physically inspected.
One problem attendant to any decommutated viewing is that most video displays have a relatively short decay period and the frame display duration is therefore limited. Accordingly, where there are many cameras interspaced within each sequence cycle, the duration of the blank period during decommutation may be excessive to allow comfortable viewing.